1. Field of the Invention
The present invention relates to a method for forming high quality boron-doped diamond films used for semiconducting electronic devices.
2. Description of the Related Art
Diamond has a large band gap 5.5 eV, and a high dielectric breakdown voltage. It also has a high thermal conductivity as compared with traditional semiconducting materials such as silicon. Therefore, diamond is expected to be used for a semiconducting material of electronic devices which can be operated in harsh environments such as high temperature.
P-type semiconducting diamond films can be synthesized by doping boron (B) in diamond films by ion implantation, or by chemical vapor deposition process (hereinafter, referred to as CVD process) using a reaction gas containing B.sub.2 H.sub.6.
Attempts have been made to fabricate electronic devices such as field effect transistors (FETs) and diodes employing p-type semiconducting diamond films.
However, in the prior art, electronic devices employing diamond films have poor electronic characteristics as compared with silicon devices, because boron-doped diamond films in the prior art have only a poor crystallinity as compared with the traditional semiconducting materials such as Si or GaAs.
It is known that the crystallinity of undoped diamond films are improved if O.sub.2 gas is added to the reaction gas in the CVD processes to grow diamond films [Y. Hirose and T. Terasawa; Jpn. J. Appl. Phys. Vol. 25, p. 519 (1986), and T. Kawata and K. Kondo; Jpn. J. Appl. Phys. Vol. 26, p. 1429 (1987)]. However, addition of O.sub.2 in the reaction gas has not been used in the formation of p-type semiconducting diamond films, because the concentration of B in the diamond films is significantly reduced by the addition of O.sub.2 due to reactions between B.sub.2 H.sub.6 and O.sub.2. As a result, the diamond films thus synthesized fail to exhibit desired electric characteristics.